Add support for reentrancy on external state variable change

Example:

```solidity
contract A{

uint public my_var = 0;

function increase() public{
// require msg.sender == C, assuming we know C
my_var += 1;
}

}

interface B{

function some_callback() external returns(uint);

}

contract C{

function buggy(A a, B b, uint v) public{
require(a.my_var() == 0);

b.some_callback();

a.increase(); // assumption that my_var == 0

}

}
```